1. Field of Invention
This invention relates to centrifugal pumps with variable speed drivers specifically to reduce pump power and energy usage in distribution of liquid through piping, coils, and cooling or heating equipment.
2. Background of the Invention
In a hydronic piping system, centrifugal pumps provide the primary force to circulate liquid through cooling or heating coils, cooling or heating equipment (such as chillers, boiler, or cooling towers), and distribution piping by overcoming water pressure drops and power losses of the coils, equipment, and piping. Originally the distribution pumps are located in a central location with the cooling or heating equipment. The cooling or heating coils are usually located in the spaces where they serve. Balancing valves and control valves are installed at the coils to modulate liquid flow by creating pressure drops and power losses across the valves.
The central distribution pumps are either constant speed or variable speed. The constant speed pumping system is usually installed with three-way control valves at the coils. The constant speed pump does not reduce pump power or energy consumption at part load. The variable speed pumping system is preferable in a large system with two-way control valves at the coils to reduce pump energy at part load. The control valves modulate the flow of liquid through the coils as required by the coil outputs. Pump head is selected from a flow path that has the highest pressure drop in the piping system. Pump speed is controlled to maintain differential pressure across the end of supply and return mains or across selected critical zones. A variable speed motor with a variable frequency drive is normally used to control the pump speed. Flow rate, pump speed, pump head, and pump power are all reduced at part load.
Variable speed pumping system can be arranged in variable-primary pumping arrangement, primary-secondary pumping arrangement or primary-secondary-tertiary pumping arrangement. In the variable-primary pumping arrangement, the primary pumps are variable speed. The primary pumps circulate liquid through a load loop and cooling or heating equipment. The load loop comprises coils, control valves, balancing valves, main supply lines, and main return lines. In the primary-secondary pumping arrangement, the primary pumps are constant speed. The primary pumps serve cooling or heating equipment in a primary source loop. The secondary pumps are variable speed and serve the load loop. A de-coupled line separates the primary source loop from the load loop. A flow meter located in the de-coupled line controls the primary pumps and the equipment to ensure that flow in the primary source loop is adequate for the load loop. The primary-secondary-tertiary pumping arrangement is used in a large campus where central cooling and heating equipment serve several buildings through central supply mains and central return mains. The primary pumps serve the central equipment in the primary source loop. The secondary pumps serve the central supply mains and central return mains. The tertiary pumps are variable speed and serve the load loops in the buildings. Variable speed pumps serving the load loops in every arrangement are located in central locations with balancing valves and control valves located at the coils.
Control valves are used in the pumping system to modulate liquid flow through the coils to satisfy temperature or pressure settings of the controlled agents. Control valves, either two way or three way, are usually selected at approximately 5 psi pressure drop when the valves are fully open at design flow. However, in actual operations the pressure drops are much higher than 5 psi. The actual pressure drops are dependent upon the valve locations in relation to the pump location. The closer a control valve is to the pump, the higher the pressure drops across it. The wide range of pressure drops makes it very difficult to select control valves to achieve linearity between the control valve positions and the coil outputs. For this reason, the balancing valves are normally installed in series with the control valves to reduce pressure drop across the control valves. Pressure drop across control valves and balancing valves create waterpower losses and energy losses in the piping system.
U.K. patent 2245967 proposed replacing control valves with pumps to overcome the difficulty of the control valve selection and operation. The proposed coil pumps are variable speed with either a centrifugal type or a positive displacement type. The positive displacement type pump is not a concern in this present invention. The centrifugal type pumps have by-pass pipes added to the cooling coil or heating coil circuits to isolate the coil circuits from the main supply line and main return line. The coil pumps circulate liquid in the coil circuits only, while the central pump is used to circulate liquid in the main supply line and main return line. The system requires balancing valves to balance flow in the main distribution lines and coil circuits.
In accordance with the present invention, the central distribution pumps, balancing valves, and modulating control valves are eliminated from the hydronic piping system. Decentralized centrifugal pumps with variable speed drivers located at the coils are utilized to circulate and regulate liquid through the load loop. Cooling or heating equipment can be located inside or outside the load loop.
The speed of each pump is independently controlled to satisfy temperature or pressure settings of a control agent served by the coil. Without the balancing valves and control valves, there will be less pressure drops and waterpower losses in the piping system. Thus, the decentralized pumping system will require less pump power and energy consumption than the central pumping system.
Accordingly, several objects and advantages of the decentralized pumping system are:
a. To provide centrifugal pumps which are driven by variable speed drivers.
b. To provide centrifugal pumps which will be located at the coils without modulating control valves at the coils.
c. To provide centrifugal pumps which will be located at the coils without balancing valves and by-passed pipes at the coils.
d. To provide centrifugal pumps which will circulate and regulate liquid through the coils, main supply line, and main return line in the load loop without central distribution pumps.
e. To provide centrifugal pumps which speeds are controlled to satisfy temperature or pressure settings of control agents served by the coils.
f. To eliminate pressure losses and waterpower losses in the balancing valves and control valves, which will reduce pump waterpower.
g. To eliminate the maintaining of differential pressure across the end of supply main and return main, which will further reduce pump waterpower at part load.
h. To reduce pump power and energy consumption.
i. To provide decentralized pump and driver in an air-conditioning unit as a single package, which will reduce equipment cost, installation cost, and space requirement.